The present invention relates to an actuator having a driving section driven by means of electro-mechanical displacing members such as a piezoelectric members, and a driven section driven by the driving section with its driving force being transmitted from the driving section.
A Japanese before-examination publication of a patent application, a publication number 2001-54289 discloses an actuator having a pair of piezoelectric members arranged orthogonally with each other, and a displacement composing member or driving piece provided at the meeting position of the piezoelectric members to be driven by the composition of the displacements of the piezoelectric members and move in a given orbit, with the movement of the displacement composing member or driving piece being transmitted, by friction therebetween, to a driven section to drive the latter in a predetermined direction.
FIG. 19 schematically illustrates a conventional actuator of the type as mentioned above. As seen in FIG. 19, the conventional actuator 700 comprises a pair of laminated type piezoelectric members 101 and 102, which are orthogonally arranged with each other, and a tip member 103 connected by adhesion to one ends of piezoelectric members 101 and 102 at the meeting position or point of the latter two. The other ends of the piezoelectric members 101 and 102 are respectively adhered to a base member 104. The driving section 110 composed of the piezoelectric members 101 and 102, the tip member 103 and the base member 104, is urged by an urging section 130 such that the tip member 103 is in press contact with a rotor 120. The urging section 130 is composed of a pair of torsion coil springs 130 and 130, each of which has a pair of arms abutting against the base member 104 to secure the position of the driving section 110.
In the conventional actuator 700, driving signals are applied to the piezoelectric members 101 and 102 with different phases so that the tip member 103 at the meeting position of the piezoelectric members 101 and 102 is driven to move in a predetermined elliptic orbit. The base member 104 is made of elastic material so that the vibration or oscillation of one of the piezoelectric members 101 and 102 is transmitted to the other of the piezoelectric members 101 and 102 through the base member 104. While the tip member 103 is driven to move in an elliptic orbit, the tip member 103 is brought into contact with the rotor 120 for a given range of the orbit, and the rotor 120 is rotated in a predetermined direction by the frictional force acting between the tip member 103 and the rotor 120. A shaft 121 is integrally connected or formed with the rotor 120 to rotate therewith, and is used as an output shaft to be connected with outside device through a link or lever or other transmission which in turn is interconnected or interlocked with a pin fixed on the shaft or a plane of the rotor that is perpendicular to the shaft.
FIG. 20 schematically illustrates another conventional actuator 800 using the same reference numerals for the parts and components that are the same or corresponding to parts and components shown in FIG. 19. With reference to FIG. 20, the actuator 800 is provided with a driving section 110 which is substantially the same in construction as that shown in FIG. 19. The base member 104 is urged by an urging section 230 to make the tip member 103 be in contact with the rotor 120. The urging section 230 comprises a compression coil spring urging the base member at its one end portion, while the other end portion of the base member 104 is supported by a fixed member 240. Accordingly, the driving section 110 makes pivotal movement around a fulcrum at a point on the base member 104, thereby driving the tip member 103 to move in an elliptic orbit. The operation of the actuator 800 shown in FIG. 20 is substantially the same as that of the actuator 700 shown in FIG. 19.
When an excessive external force is applied to the rotor 120 of the actuator 700 shown in FIG. 19, the driving section 110 which is in frictional contact with the rotor 120 is likely to swing greatly and the wires connected with the piezoelectric members are likely to break, and the swing of the driving section may affect the accuracy of the driving of the actuator.
In the actuator 800 shown in FIG. 20, the base member 104 also oscillates as an elastic member so that the oscillating state of entire driving section 110 is likely to be affected by the oscillation of the base member 104. In addition, as the construction of the driving section 110 and the urging section 230 is not symmetric with respect to a central line of the driving section 110, the elliptic orbit in which the tip member 103 moves, is different in shape with the direction of driving of the rotor 120, resulting in difference or variation in the operational characteristics of the actuator 800 such as the rotational speed of the rotor 120.